Relaying is considered for LTE Advanced as a tool to improve, for example, the coverage of high data rates for User Equipment (UE), temporary network deployment, cell edge throughput and/or to provide coverage in new cell areas. LTE Advanced supports relaying by having a Relay Node (RN) wirelessly connected to a base station (eNB) (referred to as a Donor eNB (DeNB)). In addition to serving its own ‘donor’ cell, the Donor eNB serves the RN, via a modified version of the Evolved Universal Terrestrial Radio Access (E-UTRA) radio interface. The modified interface is referred to as the ‘Un’ interface.
Each RN is provided with many aspects of a base station's functionality and is therefore capable of acting as a base station serving its own ‘relay’ cell. From the perspective of the user equipment (such as mobile telephones) in the relay cell, therefore, the RN essentially appears to be a conventional LTE base station. In addition to the base station functionality, however, the RN also supports a subset of the UE functionality including, for example, many aspects of the physical layer, Medium Access Control (MAC), radio resource control (RRC), and non access stratum (NAS) functionality, to allow it to connect wirelessly to a Donor eNB. From the perspective of the Donor eNB, therefore, the RN essentially appears to be an item of user equipment such as a mobile (cellular) telephone.
In communication systems, Location Services (LCS) may be provided to allow determination of location related information (such as a geographic position and/or velocity) for mobile telephones (or other user equipment) based, for example, on radio signal measurements. Specifically, an LCS Client entity requests the location related information for one or more target mobile telephones from an LCS Server. The LCS Client (which may be a software application) is provided within the communication system (e.g. within a mobile telephone), or externally to the communication system. The LCS Server entity employs an appropriate positioning method in order to obtain location information of the target mobile telephone(s) as requested by the LCS Client.
In LTE, both control plane and user plane positioning procedures are supported. User plane positioning is supported using a ‘Secure User Plane Location’ (SUPL) protocol between the mobile telephone for which the location related information has been requested and a so called ‘SUPL Location Platform’ (SLP) which is responsible for positioning co-ordination and calculations over the user plane. The SLP connects to the mobile telephone via a user plane data connection. Control plane positioning is supported using a so called ‘Enhanced Serving Mobile Location Centre’ (E-SMLC) which is a positioning server node that manages overall co-ordination and calculations required for obtaining location related information for a target mobile telephone (e.g. position and/or velocity of the mobile telephone). The E-SMLC exchanges data with the mobile telephone to be positioned, and the base station serving this mobile telephone, using control plane signalling.
There are three positioning methods supported for E-UTRAN. The first is called ‘Enhanced Cell ID’ (E-CID) based positioning method, which estimates the position of a target mobile telephone using knowledge about the geographical coordinates of the base station serving the mobile telephone (and/or the coordinates of the cell in which the mobile telephone is camped where these are different). The second method is called a Downlink Positioning using Observed Time Difference Of Arrival (OTDOA) method, which estimates the position of a target mobile telephone using measurements made by the mobile telephone of the UTRAN frame timing and knowledge about the geographical coordinates of the base station and/or cell serving this mobile telephone. The third positioning method is called an Assisted Global Navigation Satellite System (A-GNSS) based positioning method, which may be used by user equipment equipped with GNSS capability. Examples of GNSS include Global Positioning System (GPS) and Galileo. Providing network assistance on top of the GNSS, e.g. Assisted GPS (A-GPS), can reduce position calculation time from minutes to seconds.
LTE also supports hybrid positioning techniques using combinations of the above positioning methods.
LTE uses the LPP (‘LTE Positioning Protocol’) location protocol between a positioning server (E-SMLC/SLP) and a target mobile telephone. This is either carried in NAS signalling or as user data. In any case, LPP is transparent to the base station serving the target mobile telephone.
LTE also uses the LPPa (LTE Positioning Protocol Annex) between the E-SMLC and the base stations. LPPa messages are carried as Protocol Data Units (PDUs) within S1 signalling messages.
In order to obtain the location of a mobile telephone, the positioning function of the LCS Server requires knowledge of the geographical coordinates of the cell (i.e. the base station or relay node) serving this mobile telephone.
However, in some situations, the RN will be installed in a moving vehicle, such as on a train, bus, ship, aeroplane, or the like. Such a mobile relay node (MRN) and its cell will hence change its geographical location as the vehicle is moving and it will also change its attachment from one Donor eNB to another. In this case, even though this change of attachment occurs between a RN and the DeNBs, the mobile telephones remain served by the same, albeit ‘mobile’ cell of the same RN. In this case, however, the LCS Server is unable to provide full location services for the mobile telephones served by the MRN.
In particular, the LCS Server cannot use cell-specific geographic positioning methods for mobile telephones served by mobile relay nodes. Furthermore, this deficiency cannot always be alleviated by satellite based positioning (e.g. the A-GNSS positioning method) because such techniques cannot be relied upon for situations in which mobile telephones are served by a fast moving mobile relay node and in which the clear and uninterrupted reception from positioning satellites required for such techniques cannot be guaranteed.